Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $134.44   12.432%   $151.1536   $151.15   $151.15   $151.20  
  Purchase #2 $197.89   4.480%   $206.7555   $206.76   $206.75   $206.80  
  Purchase #3 $9.48   3.572%   $9.8186   $9.82   $9.80   $9.80  
  Purchase #4 $69.59   7.228%   $74.62   $74.62   $74.60   $74.60  
  Purchase #5 $201.96   13.224%   $228.6672   $228.67   $228.65   $228.70  
  Purchase #6 $208.76   12.365%   $234.5732   $234.57   $234.55   $234.60  
  Purchase #7 $151.49   4.556%   $158.3919   $158.39   $158.40   $158.40  
  7 purchase totals = $973.61       $1,063.9800   $1,063.98   $1,063.90   $1,064.10